From the prior art, for example from the SIEMENS brochure “TransScan TS 2000” (internal No BKW 62014 WS 10994), measuring arrangements for examining tissue sections of a patient are known, in which the electrode array is surrounded by an electrical conductor element in the form of a metal strip (“guard ring”), the metal strip and the electrodes of the electrode array being operated with an identical potential. Although this improves the detectability of conductivity inhomogeneities of the tissue section to be examined, undesired signal intensifications occur at the image edges of the impedance image.